In speed (motor) boats, the boat position and in particular the trim (pitching) of the boat is crucial in terms of cruising performance and fuel economy. Several factors such as load position, speed, the waves and wind in the sea have an effect on trim in motor boats. When the trim of the motor boat increases in relatively fast cruises, stresses occur on both the hull and the motor as the rear of the boat hull is dragged with high resistance in the sea.
Trim tabs have long been used in speed boats to stabilize the trim. Trim tabs are mounted to the transom of speed boats and they comprise a plate, the bottom surface of which structurally contacts with water, and a mounting part that can be fixed to the transom with which the plate is rotatably associated by member of a hinge joint. The stabilization of the trim is provided by an actuator (generally a piston) that can make pressure on the tab from the upper side and therefore rotate the tab. It is important how long the trim tabs extend from the bottom end of the boat transom to downwards (towards sea). Thus, as the trim tab is further from the boat to downwards, the counter pressure that the tab stabilizing the boat trim creates is higher, which provides a trim stabilization by pressing the bow of the boat towards the water. However, when trim decreases, as the boat hull will be more in contact with water, the drag and therefore the fuel consumption increase accordingly.
There are many proposals in the art with regard to trim tabs. For instance, U.S. Pat. No. 3,062,167 discloses a device which is consisted of a foil and a concave-shaped rod which is associated with the foil from one side and with different parts of the trim tabs from the two end sides.
U.S. Pat. No. 2,985,130 discloses a trim tab device that is rotated with the help of a mechanical foil arrangement.
U.S. Pat. No. 3,769,927 discloses a pair of trim tabs which can be adjusted independent of each other. The bottom end of an adjustment foil which is threaded is associated with a bracket on the tab, and as the adjustment foil is rotated, the plate rotates accordingly.
U.S. Pat. No. 5,493,990 discloses a trim stabilizer device associated with a transom of a motor boat, said device comprises a foil being tillable around its transversal axis and the foil being structurally independent from the transom; and an actuator associated with the foil for tilting thereof.
Since the trim tabs of the art are directly associated with the transom of the boat, water flow along the upper surface of the tab may not be possible. When no trim stabilization is needed, the trim tabs are lifted to transom level or to a higher level (i.e. above the water level); however, this does not contribute to the fuel economy of the boat. In this case, it is necessary to use different trim tabs depending on the physical features of the motor boat and its shallow water cruising ability, which is not practical.
The disclosed invention and the invention disclosed in U.S. Pat. No. 9,340,257 addresses the above-mentioned problems. However, the arrangement that ensures displacement of the water foil, having a trim stabilizer function as well, from the transom in vertical direction is manually operated, and the vertical arm to which the foils are connected is maintained in the desired position in the groove of a bushing mounted to the transom by the aid of a connecting member such as a bolt. If the height of the foil is subsequently changed, then the arms to which the foils are connected are to be removed and mounted to another position. On the other hand, in the trim device described in U.S. Pat. No. 9,340,257, there is also proposed a complicated and somewhat expensive proposal for tilting the foils relative to the transom of the boat, in order to space apart the foils from the hull in radial direction.